Application of the chromatographic method to determine the effective diffusivity in spherical γ-alumina pellets using convolution theorem and a fictitious column

It is shown how the chromatographic experimental technique may be applied, in combination with the use of convolution theorem, to determine the effective diffusivity of a binary pair of non-reacting gases, in spherical γ-alumina pellets (1.0 mm diameter). The experiments were performed on a packed bed (i.d. = 13.8 mm), with two different packed bed depths of 200 and 400 mm, which enabled the first and second moments for a fictitious bed length of 200 mm to be determined. The effective diffusivity of He in N₂ was 9.56 × 10⁻⁷ m² s⁻¹ for the γ-alumina pellets, and for N₂ in He was 2.31 × 10⁻⁷ m² s⁻¹. Using the parallel pore model, the apparent tortuosity factor was back-calculated and the value was found to be 2.2 –3.5 for the pellets studied.